Technical Abstract:
Soil compaction is of concern in the humid regions of the United States where declines in soil productivity are often related to compaction. Compaction can also affect the water resources of a region, by altering soil water dynamics, as well as hamper the vitality of plants by restricting root exploration. Yet, little is understood about the natural forces that ameliorate compaction. This paper reviews our current understanding and offers suggestions in the future study of soil compaction as affected by freezing and thawing. Freezing and thawing was thought by many in the post-World War II era (1950's and 1960's) to ameliorate compaction of the clayey soils in the US Corn Belt. With the advent of large machinery, however, compaction persists despite annual freezing and thawing. Indeed, more than a decade may be required to alleviate subsoil compaction as reported by several investigators. The formation of ice in soil pores as a result of subfreezing temperatures may cause soil deformation and changes in density. Soil deformation is likely to occur in fine-textured soils upon freezing owing to the formation of ice lenses. Indeed, field experiments indicate that the bulk density decreases as compacted soils freeze. As the frozen soil thaws, however, the soil reconsolidates with no apparent lasting change in density. Thus, the deformed frozen soil matrix appears to subside and consolidate during thawing. Accompanying any permanent change in soil density must be a change in soil structure or aggregation. Structural fabric created by freezing and thawing is an evolving process, taking perhaps 100 freeze-thaw cycles to create. In regions of seasonal frost, subsoil compaction may not be alleviated by natural forces for decades or centuries.